Drapable surface fastener and method of using same

ABSTRACT

A mechanical surface fastener intended to usefully conform to a three-dimensional shape comprises a stemmed web having an array of upstanding stems  10  distributed across both faces, and having through holes  11  in the web  12  positioned in the spaces between the stems. The mechanical surface fastener is used in a method of improving the impact strength of molded articles comprising sandwiching an effective amount of said fastener between layers of said foraminous reinforcing material.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0001] The invention was made with Government support under Contract No. DASG60-00-M-0119 awarded by the U.S. Army Space and Missile Defense Command. The Government has certain rights to this invention.

FIELD OF THE INVENTION

[0002] The invention relates to stemmed web fasteners. More particularly, the invention relates to improved web fasteners capable of snugly fitting the contours of a three dimensional shape.

BACKGROUND

[0003] Refastenable mechanical fastening systems based on hook and loop fasteners are well known in the art. Typically, such fastening systems comprise a web of material having a plurality of stems extending from at least one side of the web. A stem means a protrusion from a surface, such as a web, regardless of its shape, length, length-to-width ratio, geometry or other characteristics.

[0004] U.S. Pat. Nos. 4,056,593 and 4,959,265 disclose an early method of extruding polymeric webs with upstanding stems, known as stemmed webs. These early stemmed webs are formed of a single material. Only one side of the web has stems and the web is a thin continuous sheet. U.S. Pat. No. 5,951,931 discloses methods for continuously manufacturing stemmed webs using a rotating die wheel. As in other early versions, the web is a continuous sheet formed of a single material and only one side has stems.

[0005] U.S. Pat. Nos. 5,393,475 and 6,106,922 disclose methods of manufacturing stemmed webs with stems on both sides of continuous sheets of material using two different materials. The multiple components are formed together to enhance the mechanical performance properties of the mechanical fastener.

[0006] Drapability means the ability to follow the contours of a three-dimensional (3D) object without producing folds or wrinkles. Heretofore, known stemmed webs have been structures comprising webs which had unacceptable drapability for many applications. By way of example, but not by way of limitation, said applications include mechanical fastening of cloth prior to sewing, mechanical fastening of flexible devices to conform to the contours of the human body, as well as mechanical fastening of dry fiber reinforcements in place within complex mold cavities prior to and during the injection of resin into the mold cavity.

[0007] An object of the invention is to provide useful drapable mechanical fasteners for use in the sewing of cloth.

[0008] An object of the invention is to provide useful drapable mechanical fasteners for use in improving the comfort of devices that are placed against or in proximity to the body of the wearer to absorb and contain the various exudates discharged from the body.

[0009] A further object of the invention is to provide useful drapable mechanical fasteners for use in the manufacture of composite materials from dry fabrics. The many potential advantages of using dry carbon or glass fabrics for manufacturing complex 3D shapes are described in Taylor: “RTM Material Developments for Improved Processability and Performance”, SAMPE Journal, Vol. 36, No. 4, pp. 17-24 (2000).

[0010] In order to provide mechanical strength in composite structures, foraminous reinforcing material is selected from the group consisting of E-glass fibers, S-glass fibers, graphite fibers, aramid fibers, and silicon carbide fibers. This reinforcing material is placed in the cavity of a mold and injected with resin is formed from a polymeric material selected from the group consisting of polybismaleimide, polyamides, epoxys, polypropylenes, polyesters, polyethylenes, and polyphenylene sulfides. Unfortunately during the injection process viscous forces result and these cause the reinforcing fibers to move from desired locations to undesired locations. Sewing of the reinforcing material to prevent this motion tends to break fibers and reduce strength. Adhesives tend to weaken the strength of the composite.

[0011] There is a need for stemmed webs, such as mechanical fasteners, having a wider variety of properties to meet more varied applications requiring improved drapability.

SUMMARY OF THE INVENTION

[0012] The present invention is a drapable surface fastener having a web of material having two sides and a plurality of stems extending from both sides of the web, the web containing holes positioned in the spaces between the stems to permit the web to usefully conform to a three-dimensional shape. The invention can usefully stretch in all three directions so that its stretched shape snugly fits the contours of a 3D shape. Depending on the manufacturing process used to form the present invention, the holes in the web are either through holes or are holes which substantially penetrate the web.

[0013] The stems should be resistant to compression and bending, and their tips preferably are substantially pointed to permit them to penetrate easily into the interstices of a foraminous substrate, even though they may be quite supple. Preferably the points are blunt to avoid any cutting action. For most uses, each of the stems should be in height less than the thickness of the foraminous substrate used and in breadth less than 2 mm where they join to the web.

[0014] Each of the stems preferably is substantially cylindrical, rectangular, conical or pyramidal. Such stems can be given mushroom shape by softening the tip of each to create a bulbous crown. A mushroom-shaped stem can enhance the attachment of the novel drapable web fastener to a foraminous substrate, as can projections that have hooked crowns. Regardless of the shape of the stems, their tips are preferably shaped to enhance penetration into a fabric or other foraminous substrate without producing any cutting action.

[0015] The holes in the drapable surface fastener preferably are substantially rectangular or diamond shaped. Useful drapable structures can be formed by compression molding of thermoplastic films. Very thin films often block the holes so formed which are an artifact of the compression molding process and which tear when the invention is draped over a complex 3D object. A drapable stemmed web comprising through holes can preferably be continuously manufactured by the steps of:

[0016] 1. Two counter rotating die wheels having in their circumferential surfaces a multiplicity of stem-forming cavities connected together by grooves oriented in a diamond pattern;

[0017] 2. continuously supplying molten resin to a molten resin induction port adjacent to said die wheels under a predetermined resin pressure;

[0018] 3. molding the invention in an integral form along the rotating die wheels while said stem-forming cavities and said web-forming grooves are filled with said molten resin; and

[0019] 4. Separating the molded invention from said circumferential surface of said die wheels and moving the invention in a traveling path.

BRIEF DESCRIPTION OF THE DRAWING

[0020]FIG. 1 is a perspective view of a typical embodiment of the drapable stemmed web of the present invention. The drapable stemmed web has an array of upstanding stems 10 distributed across both faces, and through holes 11 in the web 12 positioned in the spaces between the stems to permit the web to usefully conform to a three-dimensional shape. In the preferred embodiment, the web as well as the stems are formed from a single tough flexible plastic, such as nylon. However, the web can consist of any other material or combination of materials that can be repeatedly bent without fracturing. Especially preferred are materials that can be formed from at least one melt processable polymeric material such as polyethylene, polypropylene, vinyl, rubber, and polyethylene-terephthalate. Also of utility are copolymers of ethylene and propylene and copolymers of ethylene and vinylacetate.

ILLUSTRATIVE ARTICLE OF USE

[0021] An illustrative and nonlimiting example of the usage of the fastening system of the present invention in an article of manufacture follows. A composite part according to the invention is produced by the process comprising the steps of:

[0022] (a) providing sheets of foraminous reinforcing material;

[0023] (b) providing a mold having a cavity;

[0024] (c) providing drapable surface fastener;

[0025] (d) selectively placing said foraminous reinforcing material and said drapable surface fastener in said mold cavity;

[0026] (e) molding a composite part from said foraminous reinforcing material and said drapable surface fastener, said part having enhanced mechanical properties in desired areas due to said foraminous reinforcing material and said drapable surface fastener being located in said desired areas.

[0027] Drapable mechanical fasteners for use in the manufacture of composite materials from dry fabrics were formed according to the invention by first compression molding nylon 6 in a two piece aluminum mold. The mold surfaces were coated with mold release spray before use. Nylon 6 pellets (Aldrich Chemical Company) or sheets of nylon 6 film (Capron®, Allied Signal Corp.) were placed in the mold, the two halves aligned and the mold placed between the heated platens of a Carver laboratory press. The temperature of the mold was raised to about 230° C. and a force of approximately 1000 pounds applied to the mold. The assembly was cooled the drapable surface fastener of the invention demolded.

[0028] Seven dry sheets of woven graphite fiber (6K, IM-7, 5-harness satin, 380 g/m² by Textile Products, Inc.) and six dry sheets of drapable stemmed webs were alternatively stacked within the inner cavity of a mold. The stems contacting the woven graphite fiber and penetrated easily into the interstices of the cloth to form a dry preform which conformed to the shape of the cavity. A commercial epoxy (Ciba epoxy MY721-HY5200) was injected into the mold and the resulting composite cured at 121° C. for 1 h and 177° C. for 3 h to manufacture the composite part of the invention.

[0029] As controls, two additional reinforced parts were molded under exactly the same conditions except the drapable mechanical fasteners of the invention were replaced by either nothing or by 5 percent by weight of fabric of a commercial tackifier resin adhesive (Epon Resin, 2002).

MECHANICAL STRENGTH IN SHEAR

[0030] The mechanical strength of said three composites was measured by first cutting test beams from along the direction of the reinforcing graphite fibers. The interlayer adhesion was measured by the interlaminar shear strength (ILSS) test according to ASTM D 3518.

[0031] The apparent interlaminar shear strength (ILSS) was calculated from linear beam theory, which relates maximum transverse shear stress to the peak load and cross-sectional area of the beam specimen. TABLE 1 Interlaminar Shear Properties of IM-7 Graphite Fiber Composites Prepared with Different Preform Assembling Methods Interply Fastening Method for Preform Composite Epoxy Resin Drapable Property None Tackifier Fastener Fastener¹ Weight Fraction 0.00 0.00 3.99 (%) Volume Fraction 0.0 0.0 5.5 (%) Tackifier² Weight Fraction 0.00 4.16 0.00 (%) Volume Fraction 0.0 5.6 0.0 (%) Epoxy Weight Fraction 22.55 15.89 22.85 (%) Volume Fraction 30.0 21.4 29.8 (%) Fiber Weight Fraction 77.45 79.95 73.14 (%) Volume Fraction 70.0 73.0 64.7 (%) Interlaminar 444 ± 41 411 ± 41 470 ± 33 Shear Strength (psi)

[0032] The incorporation of the invention was not found to significantly affect the interlaminar shear strength (ILSS) of the graphite-reinforced epoxy laminates. Table 1 shows a slight improvement in ILSS for the composites prepared according to the invention over the samples prepared with tackifier, although the difference in strength was less than one standard deviation in magnitude.

IMPACT TESTING

[0033] An illustrative and nonlimiting example of the remarkable improvement in impact strength of composites resulting from the use of the invention follows.

[0034] Falling weight impact test specimens were prepared from six-ply woven IM-7 carbon fiber fabric (5HS Weave, 6K, 380g/m², 0.024 in thick, style #4114, Textile Products, Inc.) and commercial epoxy resin MY721-HY5200 (Ciba Corp). According to the invention, drapable surface fasteners with web heights greater than the thickness of the fabric were used between the third and fourth plies to obtain mechanically stable preforms. Tackified fabric plies and non-tackified plies were used to prepare controls. The test results are summarized in Table 2. TABLE 2 Drop Weight Impact Test Results for Composites Prepared with Untreated, Tackified, and Mechanically-Fastened IM-7 Graphite Fabric Preforms and MY721-HY5200 Epoxy Matrix Resin Interply Fastening Method for Preform Composite Epoxy Resin Drapable Property None Tackifier Fastener Fastener¹ Weight Fraction 0.00 0.00 0.81 (%) Volume Fraction 0.00 0.00 1.2 (%) Tackifier² Weight Fraction 0.00 3.72 0.00 (%) Volume Fraction 0.00 5.0 0.00 (%) Epoxy Weight Fraction 22.33 17.40 17.51 (%) Volume Fraction 29.8 23.3 24.6 (%) Fiber Weight Fraction 77.67 78.88 77.88 (%) Volume Fraction 70.2 71.7 74.2 (%) Average 0.075 ± 0.076 ± 0.083 ± Laminate 0.001 0.002 0.002 Thickness (in) Specific Peak 34.0 39.6 46.8 Force (joules) Failure resin resin resin Observations cracks, cracks, cracks, fiber tears fiber tears fiber tears

[0035] The composites prepared from preforms assembled with drapable surface fasteners showed significantly higher impact resistance than the controls prepared from tackified and non-tackified plies. This property enhancement is most readily explained by the positive reinforcement provided between the laminate plies by the fasteners.

[0036] Laminates were also prepared from 6 layers of ¾ oz-E glass chopped strand mat (M127, Vetrotex-CertainTeed) and a commercial vinyl ester resin. The latter was a peroxide-initiated, thermal cure brominated vinyl ester (CORVE-8441, Cook Composites Corp.). The impact test results for these fiberglass composites based on non-woven glass reinforcements are provided in Table 3. TABLE 3 Drop Weight Impact Test Results for Composites Prepared with Untreated and Mechanically-Fastened Chopped E-Glass Strand Mat Preforms and CORVE-844 Vinyl Ester Matrix Resin Interply Fastening Method for Preform Composite Drapable Property None Fastener Fastener¹ Weight Fraction 0.00 1.62 (%) Volume Fraction 2.6 (%) Vinyl Ester Weight Fraction 33.24 31.07 (%) Volume Fraction 51.9 48.7 (%) Fiber Weight Fraction 66.76 67.31 (%) Volume Fraction 48.1 48.7 (%) Average 0.041 ± 0.053 ± Laminate 0.002 0.003 Thickness (in) Specific Peak 26.4 33.4 Force (joules) Failure resin resin Observations cracks, cracks, fiber tears fiber tears

[0037] The composites prepared from preforms assembled according to the invention with drapable web stems showed significantly higher impact resistance than the controls prepared from unmodified chopped strand mat plies. This property enhancement is most readily explained by the positive inter-ply reinforcement afforded by the nylon web arrays. An effective number of said fasteners hook into said foraminous material and greatly improve impact strength.

[0038] Accordingly, while certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in the art that various changes in the product and processes described herein may be made without departing from the scope of the invention, which is defined in the appended claims. 

What is claimed is:
 1. A drapable surface fastener having a web of material having two sides and a plurality of stems extending from both sides of the web, the web containing holes positioned in the spaces between the stems to permit the web to usefully conform to a three-dimensional shape.
 2. The drapable surface fastener of claim 1, wherein the holes are through holes and/or holes which substantially penetrate the thickness of the web.
 3. The drapable surface fastener of claim 1, wherein the holes are substantially rectangular or diamond shaped.
 4. The drapable surface fastener of claim 1, wherein the stems are substantially cylindrical, rectangular, conical, pyramidal or mushroom-shaped.
 5. The drapable surface fastener of claim 1, wherein the stems are uncapped and are substantially pointed.
 6. The drapable surface fastener of claim 1, wherein one or more of the stems have caps.
 7. The drapable surface fastener of claim 1, wherein the web is formed from at least one melt processable polymeric material.
 8. The drapable surface fastener of claim 7, wherein the polymeric material is nylon.
 9. A composite part produced by the process comprising the steps of: (a) providing sheets of foraminous reinforcing material; (b) providing a mold having a cavity; (c) providing drapable surface fastener having a web of material having two sides and a plurality of stems extending from both sides of the web, the web containing holes positioned in the spaces between the stems to permit the web to usefully conform to a three-dimensional shape; (d) selectively placing said foraminous reinforcing material and said drapable surface fastener in said mold cavity; and (e) molding a composite part from resin, said foraminous reinforcing material and said drapable surface fastener, said part having enhanced mechanical properties in desired areas due to said foraminous reinforcing material and said drapable surface fastener being located in said desired areas.
 10. The part of claim 9, said placing step includes the step of placing said foraminous reinforcing material and said drapable surface fastener in alternating layers into said mold cavity;
 11. The part of claim 9, wherein said foraminous reinforcing material is selected from the group consisting of E-glass fibers, S-glass fibers, graphite fibers, aramid fibers, and silicon carbide fibers.
 12. The part of claim 9, wherein said resin is formed from a polymeric material selected from the group consisting of polybismaleimide, polyamides, polypropylenes, polyesters, epoxys, polyethylenes, and polyphenylene sulfides.
 13. The part of claim 9, wherein said continuous strand material is a woven cloth and/or a reinforcing mat formed from continuous strand material.
 14. The part of claim 9, wherein an effective number of said stems hook into said foraminous material. 